Restoring HTC EVO 4G to stock

I bought an HTC Evo off someone and they had it rooted, but for some reason 4G isn't working. I'm not sure if it's because they rooted the phone and it now has wifi tether (I don't know too much about rooting and ROMs) but could that be the reason why 4G isn't working? If there's a way to fix it I'd appreciate it.